A woman has described the terrifying moment three men laughed and jeered as she was sexually assaulted and punched while walking home from work in Melbourne's CBD.

The 20-year-old woman, who was not identified and was referred to only as 'Addy', was attacked just before midnight on March 10 at the entrance to Eagle Alley, a laneway off Latrobe Street in Melbourne.

Addy says she didn't hear them over the loud music in her headphones until they grabbed her from behind.

"He came across aggressively from the start," she said, adding three others were "leering in the background".

"The way they were speaking was very inappropriate, very threatening."

She was then sexually assaulted by one man as three others hurled verbal abuse at her and cheered on her attacker.

Addy was punched in the face as she pulled away, but fought back, punching the man before running into a nearby park.